The authors have proposed to study three lesions in germ-free animals: burns, encephalopathy following portacaval shunt and stress ulcer. Animals will be burned, and eschar separation in germ-free animals will be investigated. Metabolic rate and oxygen utilization will be compared in germ-free and conventional animals following burn injury. Stress ulcer will be induced in rats and examined by ultramicroscopy. The effect of a variety of bacterial flora will be compared in gnotobiotic animals. Gastric secretion in germ-free and conventional rats will be compared. Hepatic encephalopathy will be induced by performing portacaval shunts in germ-free and conventional dogs and rats. The effect of various dietary substrates will be compared following shunts. Methionine will be administered to germ-free and conventional shunted rats to induce coma. A variety of other amino acids will also be tested for their effect on hepatic encephalopathy. A new model of peritonitis has been developed and will be improved and standardized. Preliminary experiments on phagocytosis and the effect of intraperitoneal antibiotics will be conducted.